In-space propulsion technologies

Proposed in-space propulsion technologies describe the propulsion technologies that could meet future space science and exploration needs. These propulsion technologies are intended to provide effective exploration of our Solar System and will permit mission designers to plan missions to “fly anytime, anywhere, and complete a host of science objectives at the destinations” and with greater reliability and safety. With a wide range of possible missions and candidate propulsion technologies, the question of which technologies are “best” for future missions is a difficult one. A portfolio of propulsion technologies should be developed to provide optimum solutions for a diverse set of missions and destinations.[1][2][3]

In-space propulsion represents technologies that can significantly improve a number of critical aspects of the mission. Space exploration is about getting somewhere safely (mission enabling), getting there quickly (reduced transit times), getting a lot of mass there (increased payload mass), and getting there cheaply (lower cost). The simple act of “getting” there requires the employment of an in-space propulsion system, and the other metrics are modifiers to this fundamental action.[1][3]

Development of technologies will result in technical solutions that improve thrust levels, Isp, power, specific mass, (or specific power), volume, system mass, system complexity, operational complexity, commonality with other spacecraft systems, manufacturability, durability, and cost. These types of improvements will yield decreased transit times, increased payload mass, safer spacecraft, and decreased costs. In some instances, development of technologies within this TA will result in mission- enabling breakthroughs that will revolutionize space exploration. There is no single propulsion technology that will benefit all missions or mission types. The requirements for in-space propulsion vary widely due according to their intended application. The described technologies should support everything from small satellites and robotic deep space exploration to space stations and human missions to Mars applications.[1][3]

The technology areas are divided into four basic groups: (1) Chemical propulsion, (2) Nonchemical propulsion, (3) Advanced propulsion technologies, and (4) Supporting technologies; based on the physics of the propulsion system and how it derives thrust as well as its technical maturity. Additionally, there may be credible meritorious in-space propulsion concepts not foreseen or reviewed at the time of publication, and which may be shown to be beneficial to future mission applications.[1]

Furthermore, the term “mission pull” defines a technology or a performance characteristic necessary to meet a planned NASA mission requirement. Any other relationship between a technology and a mission (an alternate propulsion system, for example) is categorized as “technology push.” Also, a space demonstration refers to the spaceflight of a scaled version of a particular technology or of a critical technology subsystem. On the other hand, a space validation would serve as a qualification flight for future mission implementation. A successful validation flight would not require any additional space testing of a particular technology before it can be adopted for a science or exploration mission.[1]

For both human and robotic exploration, traversing the solar system is a struggle against time and distance. The most distant planets are 4.5–6 billion kilometers from the Sun and to reach them in any reasonable time requires much more capable propulsion systems than conventional chemical rockets. Rapid inner solar system missions with flexible launch dates are difficult, requiring propulsion systems that are beyond today's current state of the art. The logistics, and therefore the total system mass required to support sustained human exploration beyond Earth to destinations such as the Moon, Mars or Near Earth Objects, are daunting unless more efficient in-space propulsion technologies are developed and fielded.[1][7]

Work being performed at the Glenn Research Center develops primary propulsion technologies that can benefit near and mid-term science missions by reducing cost, mass and/or travel times. The In-Space Program is working to develop next generation electric propulsion technologies, including Ion and Hall thrusters. Solar Sails, which are a form of propellantless propulsion, are also being developed. Solar sails rely on the naturally occurring sunlight for the propulsion energy. Other propulsion technologies being developed include advanced chemical propulsion and aerocapture.[3][8][9]